The present invention relates to an improved silencer for an internal combustion engine:
In driving a vehicle having an internal combustion engine the engine is susceptible to an accidental fire immediately after a traversing a long slope, an abrupt or sudden speed reduction, racing or a gear change. In such a state, afterburning can possibly take place in the exhaust system in some instances. In addition, a small quantity of a raw fuel may be sucked into the engine due to the continuation of the motion of the engine by inertia and may then be discharged into the exhaust system in the form of an unburned fuel, even after switching off the engine for stopping the operation of the engine. The raw fuel discharged into the exhaust system as an unburned fuel is subjected to burning in the exhaust system specially a raw fuel that stagnates in the main muffler. The raw fuel may then be subjected to explosive combustion, which causes the pressure to rise, until the raw fuel is discharged from the exhaust system at acoustic velocity. This condition has thus far constituted a serious defect not only on the respective sections of the vehicle having an internal combustion engine mounted thereon but also on the environment outside of the vehicle, as well as on the exhaust system. In other words, a tremendously harsh noise or explosion is often generated thereby, and even a flame may be blown out from the tail pipe at the outlet of the exhaust system. Obviously, such an occurrence would constitute a serious hazard.
Available thus far as methods for preventing such afterburning as set forth above have been:
(1) A METHOD FOR CAUSING AN UNBURNED, MIXED GAS THAT IS DISCHARGED FROM AN ENGINE TO BE SUBJECTED TO BURNING WHILE THE GAS STILL REMAINS IN AN UPSTREAM PORTION THEREOF IN A SOUND ABSORBING APPARATUS;
(2) EITHER AN EXHAUST MANIFOLD OR A THERMAL REACTOR IS SUITABLY SUBJECTED TO COOLING, THUS PREVENTING AN UNBURNED, MIXED GAS FROM BEING SUBJECTED TO SPONTANEOUS IGNITION; AND
(3) A FLAME AND THE SOUND OF EXPLOSION THAT RESULTS AT THE TIME OF AN EXPLOSION IN THE MIDDLE OF THE EXHAUST SYSTEM OF A SILENCER ARE CAUSED TO BE EXTINGUISHED AND ABSORBED AT THE OUTLET OF THE EXHAUST SYSTEM BY MEANS OF A FLAME-EXTINGUISHING DEVICE.
In the third one of the above-mentioned methods, one form of prior art that is presently available provides either a wire mesh, a filter, or the like positioned, at the outlet of an exhaust pipe. However, the method of this category is not designed for flame extinguishment, since the flame extinguishment structure is specifically intended for the purpose of preventing red-hot sparks of carbon from being scattered around. To meet the proposed requirement, the meshes of a wire net need be sufficiently reduced in size, which often results in clogging. Furthermore, in such a case wherein an unburned mixed gas should be subjected to explosion within a sound absorbing apparatus, a tremendously powerful flame is injected, which has thus far made it quite difficult, if not impracticable, to effect prevention of afterburning.
To cope with such a situation, introduced so far by the prior art has been a type of afterburning preventive device as is specifically intened for the purpose of overcoming the conventionally encountered difficulty mentioned above by preventing an explosion of an unburned mixed gas generated at the time of speed reduction or shut-off of an engine. A flame-extinguishing device provided with a perforated and narrow exhaust gas flow channel is positioned in a silencer that is arranged in the exhaust system of an internal combustion engine. Heat is caused to be absorbed from a flame while the flame passes through the flame-extinguishing device, whereby the flame is subjected to extinguishment. The unburned, mixed gas passing through a flow channel arranged at a position downstream of the flame-extinguishing device is thereby prevented from being subjected to inflammation. The pressure of the unburned mixed gas is prevented from rising to a level that corresponds to the acoustic velocity.
However, for the purpose of achieving greater flame-extinguishing effect and providing favorable simplification in the construction of a flame-extinguishing device, it is imperative to develope such a method wherein an effective flame-extinguishing area can be utilized to the maximum extent possible, and to eliminate several difficulties involved in the manufacture thereof, as well as to work out a new design for the construction of the flame-extinguishing device, including an interstice, that is positioned so as to compensate for irregularities resulting from thermal fluctuations in dimensions attributable to the temperature difference in the positions of the constituent components thereof, and that a flame can be prevented in an effective manner for passing through the same.